Cyber Resilience

CVE-2021-39191

MediumPublic PoC

Published: 03 September 2021

Published
03 September 2021
Modified
21 November 2024
KEV Added
—
Patch
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CVSS Score v3.1 4.7 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
EPSS Score 0.0031 54.2th percentile
Risk Priority 10 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2021-39191 is a medium-severity Open Redirect (CWE-601) vulnerability in Fedoraproject Fedora. Its CVSS base score is 4.7 (Medium).

Operationally, ranked in the top 45.8% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

Vulnerability details

mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID Connect Relying Party, authenticating users against an OpenID Connect Provider. In versions prior to 2.4.9.4, the 3rd-party init SSO functionality of mod_auth_openidc was reported…

more

to be vulnerable to an open redirect attack by supplying a crafted URL in the `target_link_uri` parameter. A patch in version 2.4.9.4 made it so that the `OIDCRedirectURLsAllowed` setting must be applied to the `target_link_uri` parameter. There are no known workarounds aside from upgrading to a patched version.

CWE(s)
CWE-601

Related Threats

No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.

Affected Assets

openidc
mod auth openidc
≤ 2.4.9.4
fedoraproject
fedora
35, 36
debian
debian linux
10.0

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

AT-2 Literacy Training and Awareness
addresses: CWE-601

Security awareness includes verifying URLs and avoiding untrusted redirects that lead to malicious sites.

SI-10 Information Input Validation
addresses: CWE-601

Validates redirect targets and URLs to ensure they conform to allowed destinations.

References